clean my POWERMAC G4 help

[JNS]

Hello everyone.

I have a;
Power Mac G4
1.25 GHz PowerPC G4
1 MB L3-cache

1.75 GB DDR SDRAM
...

and i would like to know how to completely powerclean my computer,
i know that most of the things you delete or visit somewhere on the internet, or messenger conversations still get stored somewhere inside your computer, but not possible to find or simply delete.

i want my computer to be faster etc. again because sometimes it's getting a little slower than it used to be. and i heard this could help.
also i maybe want to sell it, so i thought this would be useful then

i dont want to reinstall mac OS X again, because i have many imporant files, photos, memories, ... etc. on my computer and i am too lazy to make a huge backup.

so i was just wondering someone here could help me and give some tips, or maybe knows a good free downloadable software that deletes all the hidden files, messenger history, caches, deleted files, etc..........

Thanks in advance!

 

[JediMeister]

Onyx is a commonly used cleanup utility. It's automated but not sure if it clears the messenger history or whatever else it is you're hoping will speed up the system. Make sure you download version 1.8.5, newer or older versions will not function on 10.4